1. Field of the Invention
The present invention relates to a method of manufacturing an ink jet recording head for generating droplets of a recording liquid for use in the ink jet recording process, and an ink jet recording head manufactured by the method.
2. Description of the Prior Art
An ink jet recording head used in the ink jet recording process generally comprises outlets for ejecting droplets of a recording liquid (hereinafter called orifices), a liquid flow path, and liquid ejection energy generating portions provided in a part of the liquid flow path. A known method for producing such an ink jet recording head comprises, for example, forming tiny grooves in a substrate such as glass or a metal by a processing means such as cutting or etching, and then joining the substrate having the grooves to a suitable top plate to form a liquid flow path.
However, cutting or etching of glass or a metal had a limited processing accuracy. Moreover, an ink jet recording head produced by such a conventional method had too great roughnesses in the inside surface of the liquid flow path formed by cutting, and different etching rates applied during production led to distortions in the liquid flow path. Thus, a liquid flow path with a constant flow path resistance was difficult to obtain, and the resulting ink jet recording head was liable to vary in recording characteristics. Furthermore, etching posed the disadvantages of many manufacturing steps and increased manufacturing costs. In addition, those conventional methods had the common drawback that when a grooved plate having the liquid flow path is to be laminated to the top plate having piezoelectric elements for generating ejection energy for ejecting droplets of a recording liquid as well as driving elements such as electrothermal converting elements, the alignment of these plates was difficult, resulting in poor mass-producibility.
To solve the above-described problems, the methods described in Japanese Patent Application Laid-open Nos. 208255/1982, 208256/1982 and 154947/1986 were worked out. These methods all form a highly processable (photosensitive) resin layer on a substrate. According to these methods, the ink jet recording head, placed in the usual use environment, is always in contact with a recording liquid (generally, an ink consisting essentially of water and, in many cases, being unneutral, or an ink consisting essentially of an organic solvent). Therefore, the head structural material constituting the ink jet recording head has to be the one that does not lower in strength under the influence from the recording liquid and that does not incorporate in the recording liquid such a harmful component as will deteriorate the recording liquid characteristics. That is, there has been a demand for a structural member which maintains high weatherability and high mechanical strength over a long period of use.
On the other hand, the methods described in Japanese Patent Application Laid-Open Nos. 208255/1982 and 208256/1982 comprise pattern-forming a nozzle comprising an ink flow path and orifice portions on a substrate with the use of a photosensitive resin material, the substrate having ink ejection pressure generating elements thereon, and then joining a cover such as a glass sheet onto the nozzle. These methods, however, involved the following problems:
(i) The member for bonding the top plate drips into the ink flow path, and changes its shape.
(ii) When the substrate is cut to form the ink ejection outlets, cuttings penetrate the ink flow path, making ink ejection unstable.
(iii) Since the substrate having a hollow portion where the ink flow path has been formed is severed, some of the resulting ink ejection outlets have imperfections.
These problems decreased the yield of the ink jet recording heads produced, and made it difficult to produce an ink jet recording head having a minuscule ink flow path structure and having numerous ink ejection outlets over its large length.
As a way of preventing the above problems, the method described in the aforementioned Japanese Patent Application Laid-Open No. 154947/1986 was proposed. This method comprises forming an ink flow path pattern using a dissoluble resin, coating the pattern with an epoxy resin or the like, followed by curing the resin, severing the substrate, and then removing the dissoluble resin by dissolution. With this method, adhesion and severance are performed with the ink flow path being filled with the dissoluble resin. Thus, the above-described problems, dripping of the adhesive into the ink flow path, penetration of dust, and breakages or cracks of the ejection outlets, can be prevented.
When, as noted above, the ink flow path is to be formed by forming a dissoluble resin into an ink flow path pattern, and finally removing it by dissolution, it is required that the dissoluble resin serving as the ink flow path pattern not be dissolved or deformed by the resin coating the pattern so that a high accuracy ink flow path can be obtained. In view of this requirement, Japanese Patent Application Laid-Open No. 184868/1991 proposes a material suitable as a constituent member for an ink jet recording head for use in the above-mentioned manufacturing method. This material is a cationically polymerizable compound of an aromatic epoxy resin which is liquid at ordinary temperatures. According to the manufacturing method described in this publication, this liquid resin is used as the resin for coating the ink flow path pattern. Hence, a solvent need not be used to apply the coating resin, and consequently, the ink flow path pattern is neither dissolved nor deformed. Furthermore, this publication discloses that the cationically polymerizable compound of the aromatic epoxy resin is a resin composition causing little interaction with the ink, showing high chemical resistance, and undergoing minimal peeling.
However, the manufacturing method described in the Japanese Patent Application Laid-Open No. 184868/1991, as stated earlier, uses a resin, which is liquid at ordinary temperatures, so as to obtain a desired viscosity without using a solvent, in order to prevent the deformation of a dissoluble resin serving as an ink flow path pattern. Thus, this method was very disadvantageous in selecting materials. In addition, the way of applying this resin was also defective in that a widely used simple technique, such as solvent coating, could not be employed, since the resin itself is liquid at ordinary temperatures.
The present invention has been accomplished in light of the above problems. The object of this invention is to provide a material as a constituent member for an ink jet recording head, the material being excellent in mechanical strength, weatherability, ink resistance, and adhesion to the substrate, permitting a wide range of materials to be chosen, and being capable of easy coating, as well as to provide a manufacturing method using this material, and a high grade ink jet recording head obtained by the manufacturing method.
A method of manufacturing an ink jet recording head according to the present invention intended to attain the above object comprises the steps of:
(a) forming an ink flow path pattern on a substrate with the use of a dissoluble resin, the substrate having ink ejection pressure generating elements thereon;
(b) forming on the dissoluble resin layer a coating resin layer which will serve as ink flow path walls; and
(c) dissolving the dissoluble resin layer to form an ink flow path; wherein
for the coating resin layer there is used a cationically polymerized curing product of an epoxy resin having a structural unit expressed by the following formula (I) or (II), the epoxy resin being soluble in a solvent which does not deform the resin forming the ink flow path pattern: 
The suitable initiator for the cationic polymerization may be an aromatic onium salt.
The coating resin may contain a reducing agent for the cationic polymerization initiator. The reducing agent may be copper triflate.
The desirable epoxy equivalent of the epoxy resin may be 2000 or less.
The solvent which does not deform the resin forming the ink flow path pattern may be a non-polar solvent, and the coating resin layer may be formed by solvent coating using this solvent.
The dissoluble resin may be a positive resist or a solubility-changeable negative resist.
The above-mentioned curing product can be dissolved with the non-polar solvent for which the resist forming the ink flow path pattern shows insolubility. Therefore, the manufacturing method of the present invention enables the curing product to be applied by a simple method such as solvent coating without damaging the ink flow path pattern. Furthermore, the curing product has a high crosslinking density, and so has high mechanical strength. The curing product is also excellent in weatherability, ink resistance, and adhesion to the substrate. Thus, the use of the curing product of the present invention as a constituent material for an ink jet head makes it possible to provide a highly reliable ink jet recording head excellent in mechanical strength, weatherability, ink resistance, and adhesion to the substrate.
In the resulting ink jet recording head, the in-process coating resin layer becomes a grooved plate having a groove for forming the ink flow path on the ink ejection pressure generating elements, and openings serving as ink ejection outlets communicating with the ink flow path. The curing product that makes up the grooved plate has excellent adhesion to the substrate, as stated previously. Nevertheless, the grooved plate is fixed reliably to the substrate.
Therefore, the ink jet recording head of the present invention includes a substrate; a plurality of ink ejection pressure generating elements mounted at equal distances on one of the surfaces of the substrate; and a grooved plate being integrally fixed on the one surface of the substrate and having a groove and openings, the groove constituting an ink flow path on the ink ejection pressure generating elements, and the openings becoming ink ejection outlets communicating with the ink flow path; wherein the grooved plate is composed of a cationically polymerized curing product of an epoxy resin having a structural unit expressed by the following formula (I) or (II) 
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.